The taboo against homosexuality is especially interesting. There is not generally accepted biological explanation of homosexuality and superficially it does not appear to be adaptive. Nevertheless, evidence is accumulating that there is an inherited predisposition for homosexuality. Assuming this is the case, the taboos of the past would, paradoxically, have favoured the survival of these genes by forcing the people who carried them, against their wishes, to marry and have children.

This suggests an interesting prediction for the future. As horizontal transmission increases the taboo should lose its power and so can be expected to disappear, as indeed it is doing in many societies. Homosexuals are then free to have sex with other homosexuals, to have long-term relationships with their own sex, and not to have children at all. The short-term effect is much more overt homosexual behavior and acceptance of that behavior by everyone, but the long-term effect may be fewer genes for homosexuality.